I purchased my Velodyne CHT-10Q subwoofer back in 2009 and in the last few months it has started to make a continuous low humming sound which is distracting in low noise situations. I've tried playing with the subwoofer settings and resetting the sound settings on my Amp but the humming sound continues. Is this a common problem with subwoofers and in particular this model? Any ideas on finding a solution, other than replacing my subwoofer much appreciated.